Light-emitting or light-receiving semiconductor device and method for fabricating the same

ABSTRACT

A semiconductor device ( 10 ) having light-receiving functions can include, for example: a semiconductor element ( 1 ) formed from a p-type silicon single crystal: first and second flat surfaces ( 2, 7 ); a n-type diffusion layer ( 3 ) and a pn junction ( 4 ) thereof; a recrystallized layer ( 8 ); a reflection prevention film ( 6   a ); a negative electrode ( 9   a ) and a positive electrode ( 9   b ). A cylindrical semiconductor element can be used in place of the semiconductor element ( 1 ).

This application is a national phase application under 35 U.S.C. §371 ofInternational Application No. PCT/JP00/07359, filed Oct. 20, 2000, whichwas published May 2, 2002 as International Application No. WO 02/35612.

BACKGROUND OF THE INVENTION

The present invention relates to a method for making light-emitting orlight-receiving semiconductor device wherein a pn junction and a pair ofelectrodes are formed on a spherical or cylindrical semiconductor with apair of flat surfaces. These light-emitting or light-receivingsemiconductor devices can be used in various applications such as insolar batteries, light-emitting devices, and optical semiconductormedia.

Research has been done in technologies wherein a pn junction separatedby a diffusion layer is formed on the surface of a small, sphericalsemiconductor element formed from p-type or n-type semiconductors.Multiple spherical semiconductor elements of this type are connected inparallel to a shared electrode to be used in solar cells and opticalsemiconductor photocatalyist.

U.S. Pat. No. 3,998,659 discloses an example of a solar cell. A p-typediffusion layer is formed on the surface of an n-type sphericalsemiconductor, and multiple spherical semiconductors of this type areconnected to a shared electrode film (positive electrode) while then-type cores of these spherical semiconductors are connected to a sharedelectrode film (negative electrode).

In U.S. Pat. No. 4,021,323, p-type spherical semiconductor elements andn-type spherical semiconductor elements are arranged in a matrix andconnected to a shared electrode film. These semiconductor elements arealso placed in contact with an electrolytic fluid. This results in asolar energy converter where electrolysis of the electrolyte takes placewhen illuminated with sunlight. U.S. Pat. Nos. 4,100,051 and 4,136,436present similar solar energy converters.

As presented in PCT gazettes WO98/15983 and WO99/10935, the inventor ofthe present invention proposed a light-emitting or light-receivingsemiconductor element wherein a diffusion layer, a pn junction, and apair of electrodes are formed on a spherical semiconductor made from ap-type semiconductor and a n-type semiconductor. These multiplesemiconductor elements of this type can be connected in series, andthese series can be connected in parallel to form solar cells,photocatlyst devices involving the electrolysis of water and the like,as well as various types of light-emitting devices, color displays, andthe like.

The semiconductor elements used in this semiconductor device are smallparticles with diameters of 1-2 mm. The pair of electrodes are formed attwo apexes positioned on either side of the center of the sphericalsemiconductor element. However, the various issues remained with regardto the manufacture of the semiconductor element disclosed in these PCTgazettes.

In forming the pair of electrodes (positive and negative electrodes) onthe spherical semiconductor device, the positions at which to form theelectrodes are difficult to determine. Also, the spherical semiconductordevices tend to roll around, making handling difficult. This makesarranging multiple semiconductor devices difficult.

Also, once the pair of electrodes is formed, it is not possible toidentify which electrode is the positive electrode and which electrodeis the negative electrode. Thus, identification of the positive andnegative electrodes is difficult when multiple semiconductor elementsare arranged to connect them in series. Identifying the electrodesrequires experience, leading to reduced efficiency. Errors in positiveand negative electrode identification will lead to defective products.

OBJECTS AND SUMMARY OF THE INVENTION

The object of the present invention is to provide a sphericallight-emitting or light-receiving semiconductor device that is formedwith a pair of flat surfaces and that does not roll around easily.Another object of the present invention is to provide a spherical orcylindrical light-emitting or light-receiving semiconductor device inwhich a pair of electrodes is formed on a pair of parallel flatsurfaces. Yet another object of the present invention is to provide aspherical or cylindrical light-emitting or light-receiving semiconductordevice with an identifiable pair of electrodes. Yet another object ofthe present invention is to provide a method for making thelight-emitting or light-receiving semiconductor devices described above.

A light-emitting or light-receiving semiconductor device according tothe present invention includes: a roughly spherical semiconductorelement formed from a p-type or n-type semiconductor, the semiconductorelement being formed with parallel first and second flat surfaces atends on either side of a center thereof; a roughly spherical pn junctionformed on a surface section of the semiconductor element including thefirst flat surface; and first and second electrodes disposed on thefirst and the second flat surfaces respectively and connected to ends ofthe pn junction (claim 1).

It would be desirable an average diameter of the first and the secondflat surfaces to be smaller than a distance between the flat surfaces(claim 2). It would be desirable for the first and the second flatsurfaces to be formed with different diameters (claim 3). It would bedesirable for the semiconductor element to be made from a sphericalsemiconductor element (claim 4).

According to another aspect, the present invention provides alight-emitting or light-receiving semiconductor device including: acylindrical semiconductor element formed from a p-type or n-typesemiconductor, the semiconductor element being formed with parallelfirst and second flat surfaces at ends of the element and perpendicularto an axis thereof; a pn junction formed a surface section of thesemiconductor element including the first flat surface; and first andsecond electrodes disposed on the first and the second flat surfacesrespectively and connected to ends of the pn junction (claim 5).

It would be desirable for an average diameter of the first and thesecond flat surfaces to be smaller than a distance between the flatsurfaces (claim 6).

In the semiconductor devices in claim 2 or claim 6, the followingconfigurations would be desirable. The semiconductor element is a singlecrystal semiconductor (claim 7). The semiconductor element is a siliconsemiconductor (claim 8). The semiconductor element is a mixed-crystalsilicon and germanium semiconductor (claim 9). The semiconductor elementis a compound semiconductor formed from GaAs, InP, GaP, GaN, or InCuSe(claim 10). The semiconductor element is formed from a p-typesemiconductor; the diffusion layer is formed from a n-type diffusionlayer; a p-type diffusion layer is formed on the second flat surface;and a second electrode is disposed on a surface of the p-type diffusionlayer (claim 11). The semiconductor element is formed from a n-typesemiconductor; the diffusion layer is formed from a p-type diffusionlayer; a n-type diffusion layer is formed on the second flat surface;and a second electrode is disposed on a surface of the n-type diffusionlayer (claim 12).

A method for making a light emitting or light-receiving semiconductordevice according to the present invention includes: a first step formaking a spherical semiconductor formed from a p-type or n-typesemiconductor; a second step for forming a first flat surface at an endof the semiconductor element; a third step for forming on a surfacesection of the semiconductor element including the first flat surface adiffusion layer from a conductor different from the semiconductorelement and a roughly spherical pn junction with the diffusion layer; afourth step for forming a second flat surface by removing the diffusionlayer, the flat surface being parallel to the first flat surface andpositioned opposite from the first flat surface of the semiconductorelement; and a fifth step for forming a first and a second electrode onthe first and the second flat surface respectively, the first and thesecond electrodes being connected to ends of the pn junction (claim 13).

A method for making a light emitting or light-receiving semiconductordevice according to the present invention includes: a first step formaking a spherical semiconductor formed from a p-type semiconductor; asecond step for forming parallel first and second flat surfaces oneither end of a center of the semiconductor element; a third step forforming on a surface section of the semiconductor element including thefirst flat surface and the second flat surface a n-type diffusion layerand a roughly spherical pn junction on the diffusion layer; and a fourthstep for forming a first and a second electrode on the first and thesecond flat surface respectively, the first and the second electrodesbeing connected to ends of the pn junction (claim 14).

It would be desirable in the fourth step, for a small piece of Al, AuGa,or AuB to be placed in contact with the second flat surface and heatedand fused to form a p-type recrystallized layer passing through thediffusion layer and a second electrode continuous with therecrystallized layer (claim 15).

A method for making a light emitting or light-receiving semiconductordevice including: a first step for making a cylindrical semiconductorformed from a p-type or n-type semiconductor and forming parallel firstand second flat surfaces at ends of the semiconductor element, thesurfaces being perpendicular to an axis thereof; a second step forforming on a surface section of the semiconductor element a diffusionlayer from a conductor different from the semiconductor element and a pnjunction with the diffusion layer; and a third step for forming a firstand a second electrode on the first and the second flat surfacerespectively, the first and the second electrodes being connected toends of the pn junction (claim 16). It would be desirable in the thirdstep, for a small piece of Al, AuGa, or AuB to be placed in contact withthe second flat surface and heated and fused to form a p-type or n-typerecrystallized layer passing through the diffusion layer and a secondelectrode continuous with the recrystallized layer (claim 17).

The above, and other objects, features and advantages of the presentinvention will become apparent from the following description read inconjunction with the accompanying drawings, in which like referencenumerals designate the same elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 through FIG. 16 are drawings showing the first embodiment.

FIG. 1 is a cross-section drawing of a spherical semiconductor element.

FIG. 2 is a cross-section drawing of the semiconductor element formedwith a first flat surface.

FIG. 3 is a cross-section drawing of a semiconductor element formed witha diffusion layer and a pn junction.

FIG. 4 is a cross-section drawing of a semiconductor element formed witha second flat surface.

FIG. 5 is a cross-section drawing of a semiconductor element formed witha diffusion layer.

FIG. 6 is a cross-section drawing of a semiconductor device.

FIG. 7 is a plan drawing of a lead frame plate.

FIG. 8 is a cross-section drawing of an assembly in which semiconductordevices have been assembled with a lead frame plate.

FIG. 9 is a cross-section detail drawing of a semiconductor device and alead frame.

FIG. 10 is a plan drawing of three sets of semiconductor modules andlead frame plates.

FIG. 11 is a cross-section drawing of a semiconductor module and leadframe plate.

FIG. 12 is a cross-section drawing of a semiconductor module and leadframe plate.

FIG. 13 is a plan drawing of a semiconductor module.

FIG. 14 is a cross-section drawing of a semiconductor module.

FIG. 15 is a side-view drawing of a semiconductor module.

FIG. 16 is an equivalent circuit diagram of a semiconductor module.

FIG. 17 is a cross-section drawing of a semiconductor device accordingto an alternative embodiment 1.

FIG. 18 through FIG. 21 are drawings showing an alternative embodiment2.

FIG. 18 is a cross-section drawing of a semiconductor element formedwith first and second flat surfaces.

FIG. 19 is a cross-section drawing of a semiconductor element formedwith a diffusion layer.

FIG. 20 is a cross-section drawing of a semiconductor element formedwith a negative electrode.

FIG. 21 is a cross-section drawing of a semiconductor device.

FIG. 22 through FIG. 30 show an alternative embodiment 3.

FIG. 22 is a drawing showing a cylindrical semiconductor material and asemiconductor element.

FIG. 23 is a cross-section drawing along the XXIII—XXIII line from FIG.22.

FIG. 24 is a cross-section drawing of a semiconductor element formedwith a diffusion layer

FIG. 25 is a cross-section drawing of a semiconductor element with aflat surface removed.

FIG. 26 is a cross-section drawing of a semiconductor element formedwith a diffusion layer.

FIG. 27 is a cross-section drawing of a semiconductor device.

FIG. 28 is a plan drawing of a semiconductor module.

FIG. 29 is a cross-section drawing along the XXVIIII—XXVIIII line fromFIG. 28.

FIG. 30 is a simplified cross-section detail drawing of a semiconductordevice and lead frame.

FIG. 31 through FIG. 34 show an alternative embodiment 4.

FIG. 31 is a plan drawing of an assembly during the process of making asemiconductor module.

FIG. 32 is a front-view drawing of an assembly.

FIG. 33 is a plan drawing of a semiconductor module.

FIG. 34 is a cross-section drawing of a semiconductor module.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the figures, the embodiments of the present invention willbe described.

First, the structure of a semiconductor device according to the presentinvention will be described.

Referring to FIG. 1 through FIG. 6, there is shown a method for making alight-receiving semiconductor device 10 suited for solar cells.Referring to FIG. 6, there is shown a cross-section drawing of thelight-receiving semiconductor device 10.

Referring to FIG. 6, the light-receiving semiconductor device 10 isformed from: a semiconductor element 1 formed, for example, from ap-type semiconductor; an n-type diffusion layer 3; a pn junction 4; apair of electrodes 9 a, 9 b (a negative electrode 9 a, a positiveelectrode 9 b); a diffusion layer 8 formed from a type-p+ semiconductor;and a reflection prevention film 6 a. The semiconductor element 1 isformed from a perfectly spherical semiconductor element 1 a (see FIG. 1)formed from a p-type silicon single crystal with a diameter of, forexample, 1.5 mm. At a pair of apexes on either side of the center of thesemiconductor element 1 are formed first and second flat surfaces 2, 7,which are parallel to each other. The first flat surface 2 has adiameter of, for example, 0.6 mm. The second flat surface 7 has adiameter of, for example, 0.8 mm. The average diameter of the first flatsurface 2 and the second flat surface 7 is smaller than the distancebetween the first flat surface 2 and the second flat surface 7.

The diffusion layer 3 is formed on a section of the surface of thesemiconductor element 1 that includes the first flat surface 2. A n-typediffusion layer 3 is not formed on the second flat surface 7, andinstead a type-p+ diffusion layer 8 is formed. The diffusion layer 3 isa type n+diffusion layer formed through phosphorous diffusion and havinga thickness of 0.4-0.5 microns. The pn junction 4 (more precisely, a pn+junction) is formed roughly spherically, with the diffusion layer 3.

On the first flat surface 2, the negative electrode 9 a is formed as athin film on the surface of the diffusion layer 3 by baking a silverpaste. On the second flat surface 7, the positive electrode 9 b isformed as a thin film on the surface of the type p+ diffusion layer 8 bybaking a silver paste. The reflection prevention film 6 a is formed froma silicon oxide film 6 and is formed over the surface of the diffusionlayer 3 with the exception of the first flat surface 2 and the secondflat surface 7. The structure of the light-receiving semiconductordevice 10 will become further evident in the description of the methodfor making the light-receiving semiconductor device 10 provided below.

In this light-receiving semiconductor device 10, the roughly sphericalpn junction 4 has an photo-electrical conversion function andphoto-electrically converts received sunlight to generate ab electricpower of approximately 0.6 volts. The first flat surface 2 and thesecond flat surface 7 prevents the light-receiving semiconductor device10 from easily rolling around while allowing it to be easily graspedfrom both sides, thus making handling easier. Furthermore, since thefirst flat surface 2 and the second flat surface 7 have different sizes,the negative electrode 9 a and the positive electrode 9 b can be easilydistinguished either visually or through a sensor. This makes assemblyof the light-receiving semiconductor device 10 into semiconductormodules more efficient.

Referring to FIG. 1 through FIG. 6, a method for making thelight-receiving semiconductor device 10 presented above will bedescribed. Referring to FIG. 1, a spherical semiconductor element 1 a isproduced as a true sphere formed from a p-type silicon of single crystalwith a resistivity of approximately 1 ohm-meter. This type of sphericalsemiconductor element 1 a can be made using methods proposed in Japaneselaid-open patent publication number 10-33969 and International gazetteWO98/15983. In this method, a silicon particle is melted inside theupper end of a drop tube. The silicon particle is dropped down andsolidifies while free falling to form a spherical shape due to surfacetension, thus forming a spherical silicon single crystal. It would alsobe possible to form spherical semiconductors by performing mechanicalpolishing or the like.

Referring to FIG. 2, mechanical and chemical grinding is performed on asection of the surface of the spherical semiconductor element 1 a toform the first flat surface 2 having a diameter of approximately 0.6 mm.Referring to FIG. 3, a method known in the art is used to diffusephosphorous over the entire surface to form an n+ diffusion layer 3,resulting in a roughly spherical pn junction 4 positioned at a depth ofabout 0.4-0.5 microns from the surface of the spherical semiconductorelement 1. A silicon oxide film 5 formed on the surface during thephosphorous diffusion process is removed through etching, and heat isapplied again under an oxygen atmosphere to form a silicon oxide film 6(reflection prevention film 6 a).

Referring to FIG. 4, the side opposite from the first flat surface 2 isprocessed through mechanical and chemical grinding to form the secondflat surface 7, where the p-type silicon single crystal is exposed witha diameter of approximately 0.8 mm. The first and the second flatsurfaces 2, 7 are formed parallel at end points on either side of thecenter of the sphere. The diameter of the second flat surface 7 isformed different from the diameter of the first flat surface 2, allowingeasy identification of the negative electrode 9 a and the positiveelectrode 9 b when connecting lead frames, as described later.

Referring to FIG. 5, using a method known in the field, after formingthe first and the second flat surfaces 2, 7 and masking by the siliconoxide film 6, the boron is diffused over the surface of the p-typesilicon single crystal exposed at the second flat surface 7 to form atype-p+ diffusion layer 8 having a thickness of 0.2-0.3 microns. Theboron is diffused over the p-type layer on the second flat surface 7,and a p+n+ junction 8 a that is in contact with the type-n+ diffusionlayer 3 at the edges of the second flat surface 7 is formed inside thesilicon oxide film 6. The surface of the p+n+ junction 8 a is protectedby the silicon oxide film 6.

Referring to FIG. 6, a silver paste is applied to the surface of thediffusion layer 3 on the first flat surface 2 and the surface of thediffusion layer 8 on the second flat surface 7. The silver paste layersare heated and baked at a range of 600-800 deg C. under an oxidizingatmosphere. This results in the negative electrode 9 a and the positiveelectrode 9 b, which form low-resistance connections with the diffusionlayer 3 and the type-p+ diffusion layer 8 respectively. This completes aspherical light-receiving semiconductor device 10 suited for solarcells.

The production method described above is just one example. The processesfor forming the type-n+ diffusion layer 3, etching, forming theelectrodes, and forming the reflection prevention film can be selectedfrom conventional technologies. Also, the materials used are notrestricted to those described above, and other materials that have beenused conventionally in the past can be used. Also, apart from thesilicon oxide film described above, the reflection-prevention film canalso be a known reflection-prevention film such as a titanium oxidefilm.

Next will be described a structure of and method for making aninexpensive resin mold light-receiving semiconductor module 20 suitedfor mass production and that uses the light-receiving semiconductordevice 10 made as a solar cell as described above. Referring to FIG. 13through FIG. 16, the structure will be described first. Thelight-receiving semiconductor module 20 can, for example, include:twenty-five light-receiving semiconductor devices 10; a conductiveconnector mechanism formed from six lead frames 29 and serving toelectrically connect these twenty-five light-receiving semiconductordevices 10; a light transmitting member 31; a positive electrodeterminal 33; and a negative electrode terminal 34.

The twenty-five spherical light-receiving semiconductor devices 10 arearranged in multiple rows and multiple columns with their conductivitydirections aligned (in this embodiment five rows and five columns). Bythe conductive connector mechanism, the semiconductor devices 10 in eachcolumn are connected electrically in series, and the semiconductordevices 10 in each row are connected electrically in parallel. Theconductive connector mechanism is formed from six metallic lead frames29. A lead frame 29 is mounted between adjacent rows of semiconductordevices 10 and forms electrical connections with the electrodes 9 a, 9b. The lead frame 29 that is integral with the negative electrodeterminals 34 at the bottom end is electrically connected in parallelwith the electrodes 9 a of the semiconductors 10 of the first row. Thelead frame 29 that is integral with the positive electrode terminals 33at the top end is electrically connected in parallel with the electrodes9 b of the semiconductor devices 10 of the fifth row. These twenty-fivesemiconductor devices 10 and the conductive connector mechanism can be,for example, embedded in a light-transmitting member 31 and covered.

The light-transmitting member 31 is formed from a transparent syntheticresin such as an acrylic resin or polycarbonate. The light-transmittingmember 31 is formed with semi-cylindrical lenses 31 a for introducingsun light from either side of semiconductor devices 10. Thesesemi-cylindrical lenses 31 a serve to efficiently introduce sun light tothe columns of the semiconductor devices 10. Compared to a flatstructure, a wider orientation brings superior light collection, lightfocusing, and light guiding properties.

Referring to FIG. 16, there is shown an electrical circuit that isequivalent to the light-receiving semiconductor module 20 used in asolar cell panel as described above. The twenty-five semiconductordevices 10 form a five-by-five matrix, and the rows of semiconductordevices 10 is connected electrically in series by the six lead frames29. The rows of semiconductor devices 10 are connected electrically inparallel by the lead frames 29.

If one of the semiconductor devices 10 in this semiconductor module 20malfunctions and stops working, light-generated power will simply stopfrom the malfunctioning semiconductor device 10 while the otherfunctioning semiconductor devices 10 will continue to operate normallyand generate electricity. The generated electricity is reliably outputthrough the positive electrode terminal 33 and the negative electrodeterminal 34 so that the light-receiving semiconductor module 20 willprovide superior reliability and longevity.

Referring to FIG. 7 through FIG. 12, a method for making thelight-receiving semiconductor module 20 (solar cell module) presentedabove will be described.

First, the semiconductor devices 10 described above are made. Referringto FIG. 7, lead frame plates 21-26 formed with four openings 27 a, 27 bare made by using a die to punch thin iron-nickel alloy (56% Fe, 42% Ni)plates (thickness of approximately 0.3 mm) with silver surface platingapproximately 3 microns thick. Wide (approximately 4 mm) outer frames 28and three parallel narrow (1.5 mm) lead frames 29 are formed on the leadframe plates 21-26. The ends of the top and bottom lead frame plates 21,26 are bent beforehand at right angles, and the inner four lead frameplates 22-25 are formed as flat sheets.

Referring to FIG. 7 through FIG. 9, a conductive adhesive 30a (e.g., asilver epoxy resin) is used on the lead frames 29 of the lead frameplates 21-25 so that sets of five semiconductor devices 10 can beadhesed at an even pitch with their negative electrode 9 a facing down.

Next, a conductive adhesive 30 b is applied on the positive electrodes 9b of the semiconductor devices 10 on the lead frames 29. Referring toFIG. 8, the lead frame 29 of the lead frame plate 22 is placed on top ofthe positive electrodes 9 b of the fifteen (three sets of five)semiconductor devices 10 on the bottom layer. The lead frame plates23-26 are subsequently stacked in sequence in a similar manner, thusforming a regularly arranged five-by-five matrix with each set oftwenty-five semiconductor devices 10 being aligned with the other sets.Next, in order to provide electrical connections for the positiveelectrode 9 b and the negative electrode 9 a of each of thesemiconductor devices 10 to the lead frames 29 above and below it, aweight (not shown in the figure) having a predetermined weight is placedon the uppermost lead frame plate 26 and heat of approximately 160-180deg C. is applied to set the adhesive.

In this manner, the sets (modules) of twenty-five semiconductor devices10 are electrically connected by the six lead frame plates 21-26, andthree sets with a total of 75 semiconductor devices 10 are arranged in aregular manner between the lead frames 29 of the six lead frame plates21-26. Within the sets of 25 semiconductor devices 10, the semiconductordevices 10 in each column are connected electrically in series by thelead frames 29, and the semiconductor devices 10 in each row areelectrically connected in parallel. Referring to FIG. 9, there is showna detail drawing of a semiconductor device 10 and the lead frames 29above and below it.

Referring to FIG. 10 through FIG. 12, an assembly 30 formed from the 75semiconductor devices 10 and the six lead frame plates 21-26 is housedin a molding die (not shown in the figure) and a transparent syntheticresin (e.g., an acrylic resin or a polycarbonate) is used to form amold. This results in the five-by-five matrices of semiconductor devices10 and their corresponding lead frames 29 being embedded in and coveredby the light-transmitting members formed from the transparent syntheticresin as described above. In this manner, three sets of solar panels,i.e., light-receiving semiconductor modules 20, are formed at once. Thelight-transmitting members 31 are formed with partially cylindricallenses 31 a that focus sun light from either side of the rows of thesemiconductor devices 10.

Finally, the three sets of light-receiving semiconductor modules 20 areseparated. First, for the middle lead frame plates 22-25, cutting areas32 at the ends of the lead frames 29 extending from thelight-transmitting members 31 are cut by the molding die. For the topand bottom lead frame plates 21, 26, the cutting areas of the leadframes 29 are cut from the outer frame 28 leaving them to extend outfrom the light-transmitting member 31.

Next, different alternatives involving partial modifications to theabove embodiment will be presented.

1) Alternative Embodiment 1 (FIG. 17)

Referring to FIG. 17, a semiconductor device 10A is formed with apositive electrode 9 c, in which an aluminum ball is bonded to thesecond flat surface 7. The type-p+ diffusion layer 8 described above isomitted. To produce this semiconductor device 10, the steps illustratedin FIG. 1 through FIG. 4 are performed. Then, with the negativeelectrode 9 a bonded to the lead frame 29 with solder 11, an aluminumball having a diameter of 0.3-0.4 mm is bonded to the center of thesecond flat surface 7 via ultrasound and heat, thus forming the positiveelectrode 9 c, in the form of a bump.

It would also be possible to use a gold ball in place of the aluminumball described above. Electrodes formed via ball bonding in this mannerare suited for accurate electrode formation in a small space andlow-resistance contacts can be formed at lower temperatures comparedwith using diffusion or alloys.

Since the height of the positive electrode 9 c can be increased, it ispossible to increase the space between the lead frames 29 or the spacebetween the semiconductor device electrodes when semiconductor devicesare connected in series. Thus, a conductive adhesive can be applied tojust the positive electrode 9 c. Also, this positive electrode 9 c canbe implemented for the semiconductor device 10 described above. Also,the semiconductor device 10A described here can be used in thesemiconductor module 20 in place of the semiconductor device 10.

2) Alternative Embodiment 2 (FIG. 18-FIG. 21)

Referring to FIG. 18 through FIG. 21, a method for making asemiconductor device 10B will be described. Referring to FIG. 18, asemiconductor element 1B is formed as in the embodiment described above.First and second flat surfaces 2, 7 b are formed parallel to each otherat the two ends on either side of the center of a sphericalsemiconductor element 1 a (1.5 mm diameter) formed from a p-type siliconsingle crystal (1 ohm-m resistivity). The diameters of the first andsecond flat surfaces 2, 7 b are approximately 0.6 mm and 0.8 mmrespectively, and the average diameters of the first and second flatsurfaces 2, 7 b are smaller than the distance between the first andsecond flat surfaces 2, 7 b. Referring to FIG. 19, phosphorous isdispersed as a n-type dopant over the entire surface of thesemiconductor element 1B to form a type-n+ diffusion layer 3 having athickness of approximately 0.4-0.5 microns.

Referring to FIG. 20, the silicon oxide film generated during thediffusion of phosphorous is removed by etching. Referring to FIG. 21, asilver paste is printed on the center of the first flat surface 2 as adot having a diameter of 0.4 mm and a thickness of 0.2 mm. This silverpaste is heated under an oxidizing gas or an inert gas atmosphere at atemperature of 600-800 deg C., resulting in a negative electrode 9 athat forms a low-resistance connection with the diffusion layer 3. Next,an aluminum dot having a diameter of approximately 0.4 mm and athickness of approximately 0.3 mm is placed on the surface of the secondflat surface 7 b and is heated rapidly to a temperature of 750-850 degC. under an inert gas atmosphere or in a vacuum. As a result, thesilicon melted by the eutectic reaction of the aluminum and the silicongrows into a type p+ recrystallized layer 8 b doped with aluminum, withthe silicon single crystal serving as a seed. This is technology isknown as alloy pn-junction forming.

Since the recrystallized layer 8 b passes through the diffusion layer 3,the aluminum remaining on the surface forms a negative electrode 9 dforming a low-resistance connection with the p-type silicon singlecrystal section via the type-p+ recrystallized layer 8 b. The pnjunction 4 b is connected to the p+n+ junction 4 d. An anti-reflectionfilm (not shown in the figure) for the semiconductor element 1B is thenformed.

With this semiconductor element 1B, the type-p+ recrystallized layer 8 band the positive electrode 9 d can be formed at the same time withoutrequiring boron diffusion as in the semiconductor device 10 describedabove. Since the height of the positive electrode 9 d is increased,conductive adhesive can be applied without affecting the surface of therecrystallized layer 8 b.

In place of the aluminum described above, it would also be possible toform the recrystallized layer 8 b and the positive electrode 9 d at thesame time using gold (AuB) formed with a molecular ratio ofapproximately 99% gold and 1% boron. Alternatively gold (AuGa) with aratio of 99% gold and 1% gallium could be used. Also, this semiconductordevice 10B can be used in the semiconductor module 20 in place of thesemiconductor device 10 described above.

3) Alternative Embodiment 3 (FIG. 22-FIG. 30) Referring to FIG. 27, alight-receiving semiconductor device 10C suited for use in solar cellsincludes: a cylindrical semiconductor element 41; first and second flatsurfaces 42, 43 thereof; a n-type diffusion layer 44; a pn junction 45;a type-p+ diffusion layer 47; a silicon oxide film 46 serving as areflection prevention film; a negative electrode 49 a; and a positiveelectrode 49 b. This semiconductor device 10C is formed as a shortcylinder. While having a different shape from the semiconductor device10, the structure is similar and the following description will besimplified.

The semiconductor element 41 is formed with parallel first and secondflat surfaces 42, 43 at the ends so that they are perpendicular to theaxis. The diffusion layer 44 is formed on the outer perimeter surfaceand the first flat surface 42 of the semiconductor element 41. The pnjunction 45 is formed on the surface layer of the semiconductor element41 on top of the diffusion layer 44. The diffusion layer 44 of thesecond flat surface 42 is removed through mechanical/chemical polishing,and the type-p+ diffusion layer 47 is formed on the second flat surface43.

The negative electrode 49 a is formed on the surface of the diffusionlayer 44 on the first flat surface 42. The positive electrode 49 b isformed on the surface of the diffusion layer 47 on the second flatsurface 43. The diffusion layer 44, the pn junction 45, the diffusionlayer 47, the positive electrode 49 a, and the negative electrode 49 bare similar to those of the semiconductor device 10.

Referring to FIG. 22 through FIG. 27, a method for making thecylindrical semiconductor device 10C presented above will be described.Referring to FIG. 22 and FIG. 23, a semiconductor material 40 is formedas a thin cylinder having a diameter of 1.5 mm from a p-type siliconsingle crystal with a resistivity of approximately 1 ohm-meter. Thiscylindrical semiconductor material 40 is cut to an axial length of 1.6mm to form a short cylindrical (i.e., particle-shaped) semiconductorelement 41 having parallel first and second flat surfaces 42, 43 formedperpendicular to the axis.

This cylindrical semiconductor material formed from the p-type siliconsingle crystal can be made by growing a single crystal in the followingmanner: place a seed crystal with<111>orientation into contact withmolten silicon in a crucible, e.g., a graphite crucible, through anozzle-shaped hole at the bottom of the crucible, and pull the seedcrystal down. Since this produces a thin cylindrical shape, minimalprocessing loss is generated, making the process economical. Thediameter of the cylindrical semiconductor material 40 is not restrictedto 1.5 mm, and other diameters of approximately 1-3 mm can be used.

Referring to FIG. 24, phosphorous is diffused over the entire surface ofthe cylindrical semiconductor element 41 to form a type-n+ diffusionlayer 44 having a thickness of 0.4-0.5 microns. A pn junction 45 isformed on the outer perimeter surface and the first flat surface 42 ofthe semiconductor element 41 by means the diffusion layer 44.

Referring to FIG. 24 and FIG. 25, the silicon oxide film formed on thesurface during the phosphorous diffusion operation is removed using ahydrofluoric acid solution. Then, the semiconductor element 41 is heatedunder an oxygen atmosphere to form a silicon oxide film 46 (reflectionprevention film) over the entire surface. Then, the second flat surfaceis polished via mechanical/chemical polishing to remove the type-n+diffusion layer 44, thus forming the second flat surface 43 with thesilicon single crystal exposed.

Referring to FIG. 26, boron is diffused over the second flat surface 43after removing the silicon oxide film on the second flat surface 43.This forms the type-p+ diffusion layer 47 having a thickness of 0.1-0.2microns. As a result, the p+n+ junction 48 is formed, and the endthereof can be positioned inside the silicon oxide film so that it issealed from the outside.

Referring to FIG. 27, silver paste dots with a diameter of approximately0.5 mm and a thickness of approximately 0.2 mm are printed at the centerof the first and second flat surfaces 42, 43. These are then heated inthe same manner as in the semiconductor device 10, and the negativeelectrode 49 a and the positive electrode 49 b are disposed to formlow-resistance contact with the diffusion layer 44 and the diffusionlayer 47 respectively. This provides the cylindrical semiconductordevice 10C suited for use in solar cells. The negative electrode and thepositive electrode in this semiconductor device 10C can also be formedusing the method shown in FIG. 18 through FIG. 21.

With this semiconductor device 10C, cells are easier to manufacturecompared to spherical solar cells. Although not omnidirectional, thisdevice provides uniform orientation along the radius of thesemiconductor element. The photo-electrical conversion characteristicsprovides superior light-collecting abilities compared to flat cells.

Referring to FIG. 28 through FIG. 30, this semiconductor device 10C canbe used in place of the semiconductor device 10 in the semiconductormodule 20 described above. This provides a semiconductor module 20Asimilar to that of the semiconductor module 20. In this semiconductormodule 20A, the lead frame 29A, the negative electrode 34A, the positiveelectrode 35A, the light transmitting member 31A, and the like aresimilar to those of the semiconductor module 20, and hence are assignedlike numerals and corresponding descriptions are omitted.

4) Alternative Embodiment 4 (FIG. 31-FIG. 34) Next, a semiconductormodule 20B that has light-receiving functions and that uses thesemiconductor device 10 will be described. Referring to FIG. 33 and FIG.34, this semiconductor module 20B includes, for example: 72 (12×6)particle-shaped semiconductor devices 10 having light-receivingproperties; a conductor mechanism 50 containing eight metal ring-shapedlead frames 51-57; and a light-transmitting member 58. The 72semiconductor devices 10 are divided into 12 columns with theirconduction orientation aligned, and these are arranged in a ring patternat equal intervals along the perimeter.

The conductive connector mechanism 50 includes: a ring-shaped lead frame51 with a negative terminal 51 a at the lowest level; intermediatering-shaped lead frames 52-56; and an uppermost ring-shaped lead frame57 with a positive electrode 57 a. The ring-shaped lead frames 52-56 areflat and are formed from a similar material as the lead frame plates(21-26) from the embodiment described above. These are formed in ringswith widths of 1.5 mm. The ring-shaped lead frames 51, 57 are formedfrom material similar to the lead frame plates (21-26) and have athickness of approximately 1.0 mm.

Four negative electrode terminals 51a and four positive electrodeterminals 57 a are formed integrally with the ring-shaped lead frames51, 57, respectively. In this conductive connector mechanism 50, the sixsemiconductor devices 10 in each column are electrically connected inseries and the twelve semiconductor devices 10 in each ring areelectrically connected in parallel.

The cylindrical light-transmitting member 58 is formed as a thickcylinder from a transparent synthetic resin such as acrylic orpolycarbonate. The 12 column of semiconductor devices 10 arranged in aring formation are embedded in the perimeter wall 58 a of thelight-transmitting member 58. An irregular reflection surface 58 b isformed on the inner perimeter surface of the perimeter wall 58 a of thelight-transmitting member 58 to reflect the light transmitted throughthe perimeter wall 58 a to the semiconductor devices 10 in an irregularmanner. This irregular reflection surface 58 b is formed from multiplesmall pyramidal surfaces.

A method for making this semiconductor module 20B will be described.

Referring to FIG. 31 and FIG. 32, the ring-shaped lead frames 51-57 andthe 72 semiconductor devices 10 are made and prepared. Next, as in themaking of the semiconductor module 20, 12 semiconductor devices 10 arearranged on the top surface of the ring-shaped lead frame 51 so thattheir negative electrodes 9 a face down. A conductive adhesive is thenused to bond the devices. Next, a conductive adhesive is applied to thepositive electrodes 9 b of the 12 semiconductor devices 10, and thering-shaped lead frame 52 is mounted on top of this and bonded. Thisoperation is repeated for ring-shaped lead frame 53-57. Referring toFIG. 32, there is shown the resulting structure. A predetermined weightis placed on top of the ring-shaped lead frame 57, and heat is appliedto set the adhesive.

In other words, the 72 semiconductor devices 10 are placed with matchingconductivity orientations between the ring-shaped lead frames 51-57,forming 12 columns arranged in a ring formation at uniform intervalsalong the perimeter. The six semiconductor devices 10 in each column areconnected in series via the ring-shaped lead frames 51-57 while the 12semiconductor devices 10 in each ring are connected in parallel via thering-shaped lead frames 51-57. Referring to FIG. 31 and FIG. 32, thisresults in an assembly 60.

Next, the assembly 60 is placed in a predetermined molding die, which isthen filled with a transparent synthetic resin. Referring to FIG. 33 andFIG. 34, the light-transmitting member 58 is formed as a result in theform of a thick transparent synthetic resin cylinder. The twelve columnsof semiconductor devices 10 are embedded in the perimeter wall 58 a ofthe cylindrical light-transmitting member 58 formed from transparentsynthetic resin.

Since this semiconductor module 20B is formed as a cylinder, sun lightfrom any direction can be reliably photo-electrically converted togenerate approximately 3.6 volts between the negative electrode terminal51 a and the positive electrode terminal 57 a. Since the irregularreflection surface 58 b is formed on the inner perimeter surface of thelight-transmitting member 58, the photo-electric conversion efficiencyis improved. The difference between the outer diameter and the innerdiameter of the light-transmitting member 58 causes light with a largeincidence angle to go around inside the perimeter wall 58 a so that itis guided to a semiconductor device 10 that is far away.

Next, various modifications that can be implemented in the embodimentsdescribed above will be described.

(1) Instead of silicon, the semiconductor used in the semiconductorelements 1, 41 can be, for example, a mixed crystal semiconductor formedfrom Si and Ge, a multi-layer semiconductor, or any one of asemiconductor selected from GaAs, InP, GaP, GaN, InCuSe, or the like. Ora different type of semiconductor can be used.

(2) The semiconductor elements 1, 41 do not have to be p-type and can ben-type. In such cases, p-type diffusion layers would be formed.

(3) The diffusion layers 3, 44 and the pn junction 4, 45 can be formedusing another semiconductor film forming method, e.g., chemical vapordeposition (CVD).

(4) The reflection prevention films 6 a, 46 can be an insulative filmother than silicon oxide film, e.g., titanium oxide. Also, when formingthe electrodes 9 a, 9 b, 49 a, 49 b, a metal paste other than silverpaste can be used as the electrode material, e.g., aluminum or gold.When bonding the semiconductor devices 10 to the lead frame 29, soldercan be used in place of a conductive resin.

(5) Instead of using a light-transmitting member in the semiconductormodules 20, 20A, a reinforcement glass can be mounted on either side ofthe semiconductor module, transparent ethylene vinyl acetate (EVA) resinor the like can be poured between the reinforcement glasses, and theends can be sealed.

(6) In place of the semiconductor devices 10, the semiconductor modules20, 20A, 20B can use the semiconductor device 10A, 10B, or 10C.

The number or arrangement of the semiconductor devices mounted on thesemiconductor modules 20, 20A, 20B are not restricted to what isdescribed in the above embodiments and can be defined freely.

(7) The semiconductor modules described above are presented assemiconductor modules having light-receiving functions. However, thesemiconductor module of the present invention can be implemented in asimilar manner for semiconductor modules having light-emittingfunctions. In such cases, semiconductor devices having light-emittingfunctions (spherical semiconductor devices, cylindrical semiconductordevices, or particle-shaped semiconductor devices) must be used.

For these light-emitting semiconductor devices, the various types ofspherical light-emitting diodes proposed by the present inventor inWO98/15983 and WO99/10935 can be used, as well as various other types oflight-emitting diodes.

These types of semiconductor modules with light-emitting functions canbe used in planar illumination devices, various types of displaydevices, e.g., monochrome and color displays, and the like.

(8) The present invention is not restricted to the embodiments describedabove, and various other modifications can be made to the embodimentswithout departing from the spirit of the present invention.

Having described preferred embodiments of the invention with referenceto the accompanying drawings, it is to be understood that the inventionis not limited to those precise embodiments, and that various changesand modifications may be effected therein by one skilled in the artwithout departing from the scope or spirit of the invention as definedin the appended claims.

What is claimed:
 1. A light-emitting or light-receiving semiconductordevice comprising: a roughly spherical semiconductor element formed fromone of a p-type and a n-type semiconductor, said semiconductor elementbeing formed with parallel first and second flat surfaces at ends oneither side of a center thereof; a diffusion layer formed on a surfacesection of said semiconductor element including said first flat surface;a roughly spherical pn junction formed on said diffusion layer; andfirst and second electrodes disposed on said first and said second flatsurfaces respectively and connected to ends of said pn junction.
 2. Alight-emitting or light-receiving semiconductor device, according toclaim 1, wherein an average diameter of said first and said second flatsurfaces is smaller than a distance between said flat surfaces.
 3. Alight-emitting or light-receiving semiconductor device, according toclaim 1, wherein said first and said second flat surfaces are formedwith different diameters.
 4. A light-emitting or light-receivingsemiconductor device, according to claim 2, wherein said semiconductorelement is made from a spherical semiconductor element.
 5. Alight-emitting or light-receiving semiconductor device as described inclaim 2 wherein said semiconductor element is a single crystalsemiconductor.
 6. A light-emitting or light-receiving semiconductordevice as described in claim 2 wherein said semiconductor element is asilicon semiconductor.
 7. A light-emitting or light-receivingsemiconductor device as described in claim 2 wherein said semiconductorelement is a mixed-crystal silicon and germanium semiconductor.
 8. Alight-emitting or light-receiving semiconductor device as described inclaim 2 wherein said semiconductor element is a compound semiconductorformed from at least one of a group consisting of GaAs, InP, GaP, GaN,and InCuSe.
 9. A light-emitting or light-receiving semiconductor deviceas described in claim 2 wherein: said semiconductor element is formedfrom a p-type semiconductor; said diffusion layer is formed from ann-type diffusion layer; a p-type diffusion layer is formed on saidsecond flat surface; and a said second electrode is disposed on asurface of said p-type diffusion layer.
 10. A light-emitting orlight-receiving semiconductor device as described in claim 2 wherein:said semiconductor element is formed from an n-type semiconductor; saiddiffusion layer is formed from a p-type diffusion layer; an n-typediffusion layer is formed on said second flat surface; and said secondelectrode is disposed on a surface of said n-type diffusion layer.
 11. Alight-emitting or light-receiving semiconductor device comprising: acylindrical semiconductor element formed from one of a p-type and n-typesemiconductor, said semiconductor element being formed with parallelfirst and second flat surfaces at ends of said element and perpendicularto an axis thereof; a diffusion layer formed on a surface section ofsaid semiconductor element including said first flat surface; a roughlycylindrical pn junction formed on said diffusion layer; and first andsecond electrodes disposed on said first and said second flat surfacesrespectively and connected to ends of said pn junction.
 12. Alight-emitting or light-receiving semiconductor device, according toclaim 11, wherein an average diameter of said first and said second flatsurfaces is smaller than a distance between said flat surfaces.
 13. Alight-emitting or light-receiving semiconductor device as described inclaim 12 wherein said semiconductor element is a single crystalsemiconductor.
 14. A light-emitting or light-receiving semiconductordevice as described in claim 12 wherein said semiconductor element is asilicon semiconductor.
 15. A light-emitting or light-receivingsemiconductor device as described in claim 12 wherein said semiconductorelement is a mixed-crystal silicon and germanium semiconductor.
 16. Alight-emitting or light-receiving semiconductor device as described inclaim 12 wherein said semiconductor element is a compound semiconductorformed from at least one of a group consisting of GaAs, InP, GaP, GaN,and InCuSe.
 17. A light-emitting or light-receiving semiconductor deviceas described in claim 12 wherein: said semiconductor element is formedfrom a p-type semiconductor; said diffusion layer is formed from an-type diffusion layer; a p-type diffusion layer is formed on saidsecond flat surface; and a second electrode is disposed on a surface ofsaid p-type diffusion layer.
 18. A light-emitting or light-receivingsemiconductor device as described in claim 12 wherein: saidsemiconductor element is formed from a n-type semiconductor; saiddiffusion layer is formed from a p-type diffusion layer; a n-typediffusion layer is formed on said second flat surface; and a secondelectrode is disposed on a surface of said n-type diffusion layer.
 19. Amethod for making a light emitting or light-receiving semiconductordevice comprising: a first step for making a spherical semiconductorelement formed from one of a p-type and n-type semiconductor; a secondstep for forming a first flat surface at an end of said semiconductorelement; a third step for forming on a surface section of saidsemiconductor element including said first flat surface a diffusionlayer from a conductor different from said semiconductor element and aroughly spherical pn junction on said diffusion layer; a fourth step forforming a second flat surface by removing said diffusion layer, saidflat surface being parallel to said first flat surface and positionedopposite from said first flat surface of said semiconductor element; anda fifth step for forming a first and a second electrode on said firstand said second flat surface respectively, said first and said secondelectrodes being connected to ends of said pn junction.
 20. A method formaking a light emitting or light-receiving semiconductor devicecomprising: a first step for making a spherical semiconductor elementformed from a p-type semiconductor; a second step for forming parallelfirst and second flat surfaces on either end of a center of saidsemiconductor element; a third step for forming on a surface section ofsaid semiconductor element including said first flat surface and saidsecond flat surface a n-type diffusion layer and a roughly spherical pnjunction on said diffusion layer; and a fourth step for forming a firstand a second electrode on said first and said second flat surfacerespectively, said first and said second electrodes being connected toends of said pn junction.
 21. A method for making a light emitting orlight-receiving semiconductor device as described in claim 20, whereinin said fourth step, a small piece of at least one of a group consistingof Al, AuGa, and AuB is placed in contact with said second flat surfaceand heated and fused to form a p-type recrystallized layer passingthrough said diffusion layer and a second electrode continuous with saidrecrystallized layer.
 22. A method for making a light emitting orlight-receiving semiconductor device comprising: a first step for makinga cylindrical semiconductor element formed from at least one of a p-typeand n-type semiconductor and forming parallel first and second flatsurfaces at ends of said semiconductor element, said surfaces beingperpendicular to an axis thereof; a second step for forming on a surfacesection of said semiconductor element including said first flat surfacea diffusion layer from a conductor different from said semiconductorelement and a pn junction on said diffusion layer; and a third step forforming a first and a second electrode on said first and said secondflat surface respectively, said first and said second electrodes beingconnected to ends of said pn junction.
 23. A method for making a lightemitting or light-receiving semiconductor device as described in claim22 wherein in said third step, a small piece of at least one of a groupconsisting of Al, AuGa, and AuB is placed in contact with said secondflat surface and heated and fused to form one of a p-type and an n-typerecrystallized layer passing through said diffusion layer and a secondelectrode continuous with said recrystallized layer.
 24. A lightemitting or light receiving semiconductor device comprising: asemiconductor element formed from one of a p-type and a n-typesemiconductor, said semiconductor element being formed with parallelfirst and second flat surfaces at ends on either side of a centerthereof; said semiconductor element having a shape selected from thegroup comprising roughly spherical and cylindrical; a diffusion layerformed on a surface section of said semiconductor element including saidfirst flat surface; a pn junction formed with said diffusion layer; andfirst and second electrodes disposed on said first and said second flatsurfaces respectively and connected to ends of said pn junction.
 25. Amethod for making a light emitting or light receiving semiconductordevice comprising: a first step for making a semiconductor elementformed from one of a p-type and n-type semiconductor, said semiconductorelement having a shape selected from the group comprising roughlyspherical and cylindrical; a second step for forming a first flatsurface at an end of said semiconductor element; a third step forforming on a surface section of said semiconductor element includingsaid first flat surface a diffusion layer from a conductor differentfrom said semiconductor element and a pn junction formed with saiddiffusion layer; a fourth step for forming a second flat surface byremoving said diffusion layer, said second flat surface being parallelto said first flat surface and positioned opposite from said first flatsurface of said semiconductor element; and a fifth step for forming afirst and a second electrode on said first and said second flat surfacerespectively, said first and said second electrodes being connected toend of said pn junction.